Apparatuses for measuring out by weight are known that generally comprise carousel having a rotatably mounted platform supporting a series of weighing members above which filling nozzles are disposed that are connected to a feed member. The opening and closing of the filling nozzles is controlled by a weighting processor unit connected to the weighing members. Receptacles to be filled are brought one after another onto a weighing member and they are filled while the platform is rotating, prior to being removed therefrom.
Given the space occupied by the devices for installing empty receptacles and for removing receptacles that have been filled, filling cannot be performed over an entire turn of the platform, but only over a fraction of a turn. In general, filling takes place over an angular sector of about 270.degree. which corresponds to a maximum filling time that is a function of the speed of rotation of the platform. This speed of rotation of the platform is itself given by the throughput desired from the installation as a whole. In present systems, it is common to require an installation to have a filling throughput that may be as high as several hundred receptacles per minute.
In present systems, the weight of substance inserted into a receptacle is controlled either by timing or by weighing. When control is by timing, a first estimate is made of the time required for inserting a determined weight of substance into a receptacle, then the weight actually inserted into receptacles is checked, and the length of time the filling nozzles are opened is adjusted as a function of the difference between the weight as actually measured and the reference weight desired in the receptacle. Thus, in order to be able to adjust the actual filling time it is necessary to provide an adjustment period of time at the end of filling corresponding to some angular sector and during which the filling nozzles may be opened or closed. This adjustment period of time is used to a greater or lesser extent depending on whether filling actually takes place more slowly or more quickly than initially expected. This adjustment period of time must be taken from the maximum available filling time such that the actual filling time is less than the maximum filling time.
When filling is directly controlled by weighing, the weighing member switches off the filling operation when the weight inserted in the receptacle reaches a determined threshold. The actual time taken for filling therefore varies, in particular as a function of the viscosity of the substance. Under such circumstances, it is thus also necessary to provide an adjustment period of time at the end of filling during which the filling nozzles are closed or are kept open depending on whether or not the reference weight threshold has been reached. As before, it is therefore not possible to make continuous use of the maximum filling time.
In either case, it is therefore necessary to provide the platform with a speed of rotation that allows normal filling to take place over an angular sector that is smaller than the maximum angular sector, e.g. over an angular sector of 240.degree. rather than 270.degree.. Given that the maximum flow rate through a filling nozzle is necessarily limited, the existence of an adjustment period of time necessarily puts a limit on the speed of rotation of the platform so as to ensure that enough time is available for normal filling while travelling through an angle of 240.degree.. The throughput of the installation is thus correspondingly limited.
In addition, when the substance is semisolid, it is necessary to exert pressure thereon to cause it to leave the filling nozzle. The jet of substance transmits this pressure to a greater or lesser extent to the top of the substance already in the receptacle, depending on the viscosity of the substance, and thereby giving rise to an error in the data obtained by the weighing member. When filling is directly controlled by weighing, i.e. When the filling nozzle is closed on the weight reaching a determined threshold, such errors can be unacceptably large.
The object of the invention is to provide a method and an apparatus enabling filling throughput to be increased relative to existing devices, without loss of accuracy.